1. Field of the Invention
The present invention relates to a chemical mechanical polishing apparatus.
Priority is claimed on Japanese Patent Application No. 2009-024877, filed Feb. 5, 2009, the content of which is incorporated herein by reference.
2. Description of the Related Art
As well known, a CMP (Chemical Mechanical Polishing) machine is used for polishing a workpiece, such as a surface of a semiconductor wafer that is required to be flat. For example, Japanese Patent Laid-Open Publication No. 2006-080138 discloses a conventional CMP apparatus.
FIGS. 6 and 7 illustrate an example of a conventional CMP apparatus 1. FIGS. 6 and 7 are cross-sectional and plane views illustrating the CMP apparatus 1, respectively.
As shown in FIGS. 6 and 7, the conventional CMP apparatus 1 schematically includes: a rotatable circular platen 3 that is placed in a waste container 2 and has a predetermined thickness; a polishing pad 4 attached onto the platen 3; a carrier 6 that presses a workpiece 5 to be polished against the polishing pad 4; a slurry supplier 7 that supplies a slurry onto the polishing pad 4; and a dresser 8 that planarizes the polishing pad 4.
The waste container 2 has an outlet 9 on a bottom surface 2a thereof. A side wall 2b of the waste container 2 is perpendicular to a bottom wall 2a of the waste container 2. The outlet 9 is provided for removing slurry which is dripped on the polishing pad 4 and then is dropped on the waste container 2.
The platen 3 has a predetermined thickness and is circular in plane view (i.e., when viewed in a direction perpendicular to upper and bottom surfaces of the platen 3). The platen 3 is rotatable around a circumference thereof using an apparatus (not shown). The polishing pad 4 is attached onto the platen 3.
The polishing pad 4 polishes the workpiece 5 by grinding against the workpiece 5. The polishing pad 4 may be made of any material, such as a foamable resin, a non-foamable resin, or a nonwoven fabric, as long as the workpiece 5 can be polished.
The carrier 6 schematically includes a polishing head 11 and a retainer 12. The polishing head 11 is rotatable around a circumference thereof and is circular in plane view. The polishing head 11 can press the workpiece 5 held by the retainer 12 against the polishing pad 4.
The retainer 12 is disposed between the polishing head 11 and the polishing pad 4 to hold the workpiece 5. Specifically, the retainer 12 is a ring-shaped board having a predetermined thickness and has space 13 in the center thereof. A compression chamber 15 defined by a membrane 14 is provided in the space 13. The retainer 12 holds the workpiece 5 under the compression chamber 15 in the space 13.
When the compression chamber 15 is compressed, the membrane 14 downwardly expands. The membrane 14 is made of, for example, neoprene rubber. A compression unit 16 connects to a duct different from one connected to the compression chamber 15, and is used for adjusting expansion of the membrane 14.
The slurry supplier 7 drips, in the center region of the polishing pad 4, slurry (not shown) that is an abrasive including grains for polishing the workpiece 5 on the polishing pad 4. A slurry can be selected according to the workpiece 5. For example, a slurry including SiO2, Al2O3, CeO2, and the like as grains can be used.
The dresser 8 is provided for maintaining the planarity and polishing efficiency of the polishing pad 4. Therefore, the dresser 8 is not limited to a specific configuration as long as the dresser 8 can planarize the polishing pad 4 from the periphery to the center thereof.
Hereinafter, a method of polishing the workpiece 5 using the CMP apparatus 1 is explained.
Firstly, the workpiece 5 to be polished is held by the retainer 12 with a target surface of the workpiece 5 downwardly facing. Then, the polishing head 11 is moved above the polishing pad 4 while the workpiece 5 is held.
Then, the polishing pad 4 and the polishing head 11 are rotated, and the compression chamber 15 is compressed by injecting air thereinto, so that the membrane 14 expands and therefore the workpiece 5 is pressed against the polishing pad 4.
Then, the slurry supplier 7 supplies a slurry onto the polishing pad 4. Thus, the polishing pad 4 is grinded against the workpiece 5, thereby polishing the workpiece 5.
When the workpiece 5 is polished by the conventional CMP apparatus 1, the certain number of workpieces 5 are scratched. FIG. 4 is a graph illustrating the relationship between the rotation number of the platen 3 and the number of defective wafers when wafers are used as the workpieces 5.
As understood from FIG. 4, the number of defective wafers increases as the rotation number of the platen 3 increases, indicating that dried-and-solidified slurry drops on the polishing pad 4, thereby causing the workpiece 5 to be scratched.
In other words, the slurry dripped in the center region of the polishing pad 4 spreads over the surface of the polishing pad 4 and then escapes from the periphery of the polishing pad 4. Then, the slurry hits the side wall 2b of the waste container 2 due to centrifugal force generated by the rotating polishing pad 4, and is removed from the outlet 9.
When the slurry hits the side wall 2b of the waste container 2, a part of the slurry is dispersed in the air and attached onto a wall of a processing container of the CMP apparatus 1 (not shown) and surfaces of the polishing head 11, and then is dried and solidified in some cases.
Then, the dried-and-solidified slurry naturally drops, but a part of the slurry drops on the polishing pad 4. For this reason, foreign matters are present on the polishing pad 4, thereby causing the workpiece 5 to be scratched.